Fetal Development : Week 7
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Gestational Week 7 (Conceptual Week 5):

The embryo is now about 1 centimeter ( 0.4  inches) long . This week the hands and feet are forming as well as the mouth and face. Your health care provider should be able to detect a heart beat and movement using an ultrasound during this time.

During this week the placenta assumes production of progesterone from the corpus luteum.  Removal of the corpus luteum before the 7th week will usually result in spontaneous abortion.

Increasing production of progesterone and estrogen are believed to be responsible for recurrent migraine headaches and mood swings during this time. Avoiding substances that may trigger migraines such as cured meats and the food additive monosodium glutamate (MSG) may help prevent migraines in some women. Nonmedical treatment of headache includes cold compresses to the head and sleep in a cool darkened room. First line medical treatment of headaches during pregnancy  is usually with  acetaminophen (Tylenol) or acetaminophen with caffeine. Mood swings will typically decrease by the 10th week, but may recur during the third trimester.

Nausea may increase during this week and appears to correspond to increasing levels of the hormone beta-human chorionic gonadotropin.  Some dietary changes  may help to reduce the nausea. A more severe form of nausea and vomiting, called hyperemesis gravidarum, may require medical treatment.

Undetected ectopic pregnancies (pregnancies outside of the uterus such as a tubal pregnancy) often present during the 6th the 8th weeks of pregnancy. You should inform your health care provider if you have any of the following symptoms:

Symptoms of Possible Ectopic Pregnancy

  • Abdominal pain
  • Vaginal bleeding
  • Dizziness or fainting
  • Shoulder pain
  • Passage of tissue

Ectopic pregnancy is diagnosed using ultrasonography and quantitative measurements of  beta-human chorionic gonadotropin (beta-HCG). Ectopic pregnancy is suspected if an intrauterine gestational sac is not seen using transabdominal ultrasonography with a beta HCG of  6,500 mIU /mL (6,500 IU/L) or greater, or  an intrauterine gestational sac is not seen using transvaginal ultrasonography and the beta-HCG is  1,500mIU/mL (1,500 IU/L) or greater.

 

Table 1. Gestational Age When Organ Systems are Most Sensitive to Birth Defects.

Developmental stage Embryonic Stage Fetal Stage
Gestational  Age  (Months)                               1                                2                             3
Gestational  Age (Weeks) 1 2 3 4 5 6 7 8 9 10 11 12 13
Postconception Age  (weeks) 0 0 1 2 3 4 5 6 7 8 9 10 11
Developing Organ(s)  
CNS    
Heart    
Ear    
Eyes    
Limbs  
Lip  
Palate    
Teeth    
External genitals    
Weight ounces 1.3 1.6 2 2.6
grams 35 45 58 73
Length inches 0.16 0.39 0.63 0.91 1.22 1.61 2.13 2.64
centimeters 0.4 1 1.6 2.3 3.1 4.1 5.4 6.7

The red bars in the table show the gestational age when different organ systems are most sensitive to major birth defects in that organ system. The gray bars show the gestational age when different organ systems are sensitive to functional defects and minor malformations.

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REFERENCES

1. Obstetric Ultrasound: Chervenak FA and Gabbe SG Assessment of Fetal Growth and Anatomy  In Gabbe SG et al ed: Obstetrics - Normal and Problem Pregnancies, 4th ed. New York.: Churchill Livingstone 2002
2. Liu JH. Endocrinology of pregnancy. In Maternal-fetal Medicine: principles and practice. Resnik R, Creasy K, Iams JD ed. 5th ed Philadelphia: W.B. Saunders Company 2004
3. Moore KL, Persaud TVN, The developing human: clinically oriented embryology, 7th edition, Saunders, 2003:520.
4. Sandler TW. Langmans’s Medical Embryology, 7th ed.Baltimore:  William and Wilkins; 1995
5. Hadlock FP, et al. In utero analysis of fetal growth: a sonographic weight standard.Radiology. 1991;181:129-33.PUBMED
6.  Hadlock FP, et al Fetal crown-rump length: reevaluation of relation to menstrual age (5-18 weeks) with high-resolution real-time US.Radiology. 1992;182(2):501-5. PUBMED
7. Melhado EM, Headache during gestation: evaluation of 1101 women.Can J Neurol Sci. 2007;34(2):187-92. PUBMED
8. Stenchever MA, Droegemueller W, eds. Comprehensive Gynecology. 4th ed. St. Louis: Mosby, 2001 page 460-61

Reviewed by Mark Curran, M.D. FACOG

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